HTTP decorator

The @http decorator can be used for the tasks to be executed on a remote Web Service via HTTP requests. In order to create HTTP tasks, it is obligatory to define HTTP resource(s) in resources and project files (see HTTP configuration). Following code snippet (Code 82) is a basic HTTP task with all required parameters. At the time of execution, the runtime will search for HTTP resource from resources file which allows execution of ‘service_1’ and send a GET request to its ‘Base URL’. Moreover, python parameters can be added to the request query as shown in the example (between double curly brackets).

Code 82 HTTP Task example.

from pycompss.api.task import task
from pycompss.api.http import http

@http(service_name="service_1", request="GET",
      resource="get_length/{{message}}")
@task(returns=int)
def an_example(message):
    pass

For POST requests it is possible to send a parameter as the request body by adding it to the payload arg. In this case, payload type can also be specified (‘application/json’ by default). If the parameter is a FILE type, then the content of the file is read in the master and added to the request as request body.

Code 83 HTTP Task with POST request.

from pycompss.api.task import task
from pycompss.api.http import http

@http(service_name="service_1", request="POST", resource="post_json/",
      payload="{{payload}}", payload_type="application/json")
@task(returns=str)
def post_with_param(payload):
    pass

For the cases where the response body is a JSON formatted string, PyCOMPSs’ HTTP decorator allows response string formatting by defining the return values within the produces parameter. In the following example, the return value of the task would be extracted from ‘length’ key of the JSON response string:

Code 84 HTTP Task with return value to be extracted from a JSON string.

from pycompss.api.task import task
from pycompss.api.http import http


@http(service_name="service_1", request="GET",
      resource="produce_format/{{message}}",
      produces="{'length':'{{return_0}}'}")
@task(returns=int)
def an_example(message):
    pass

Note that if the task has multiple returns, ‘return_0’, ‘return_1’, return_2, etc. all must be defined in the produces string.

It is also possible to take advantages of INOUT python dicts within HTTP tasks. In this case, updates string can be used to update the INOUT dict:

Code 85 HTTP Task with return value to be extracted from a JSON string.

@http(service_name="service_1", request="GET",
      resource="produce_format/test",
      produces="{'length':'{{return_0}}', 'child_json':{'depth_1':'one', 'message':'{{param}}'}}",
      updates='{{event}}.some_key = {{param}}')
@task(event=INOUT)
def http_updates(event):
    """
    """
    pass

In the example above, ‘some_key’ key of the INOUT dict param will be updated according to the response. Please note that the {{param}} is defined inside produces. In other words, parameters that are defined inside produces string can be used in updates to update INOUT dicts.

Important

Disclaimer: Due to serialization limitations, with the current implementation, outputs of regular PyCOMPSs tasks cannot be passed as input parameters to http tasks.

Disclaimer: COLLECTION_* and DICTIONARY_* type of parameters are not supported within HTTP tasks. However, Python lists and dictionary objects can be used.